Process and system for obtaining a gaseous pressure product by the cryogenic separation of air

ABSTRACT

A process and system are used for obtaining a gaseous pressure product by cryogenic separation of air. In the normal operation, charge air is condensed, cooled and fed to a distillation column system; a product fraction is withdrawn-in a liquid condition from the distillation column system, and is introduced into a liquid tank; product liquid is removed from the liquid tank, is pressurized in a pump set in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a first heat transfer medium flow, and is withdrawn as a gaseous pressure product. In an emergency operation, product liquid is removed from the liquid tank, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a second heat transfer medium flow, and is withdrawn as a gaseous pressure product. In a bypass operation, the product fraction withdrawn in the liquid condition from the distillation column system is guided past the liquid tank; is brought via the pump set is brought in the liquid condition to an increased pressure; is evaporated in an indirect heat exchange, and is withdrawn as a gaseous pressure product.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Application No.: 10 2004 015 348.5 filed on Aug. 17, 2004, the disclosure of which is expressly incorporated by reference herein.

The invention relates to a process for obtaining a gaseous pressure product by the cryogenic separation of air. Preferred embodiments of the invention relate to such a process and system wherein, in a normal operation: charge air is condensed, cooled and fed to a distillation column system, a product fraction is withdrawn in a liquid state from the distillation column system and is introduced into a liquid tank, product liquid is removed from the liquid tank via a pump set having one or more parallel-connected individual pumps, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a first heat transfer medium flow, and is withdrawn as a gaseous pressure product, and wherein, in an emergency operation: product liquid is removed from the liquid tank, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a second heat transfer medium flow and is withdrawn as a gaseous pressure product,

Processes and systems for the cryogenic separation of air are known, for example, from Hausen/Linde, “Tieftemperaturtechnik” (“Cryogenics”), 2nd Edition 1985, Chapter 4 (Pages 281 to 337). The distillation column system of the invention may be constructed as a single-column system for the nitrogen-oxygen separation, as a two-column system (for example, as a classical Linde double-column system) or as a three-column or multicolumn system. In addition to the columns for the nitrogen-oxygen separation, it may have further devices for obtaining other air constituents, particularly noble gases, such as argon.

The process of the invention can be classified as one of the internal-condensation processes. This means that, in the normal operation, at least one of the products of the distillation column system (for example, nitrogen from the single column of a single-column system, from the high-pressure column of a two- or three-column system and/or from the MDS or intermediate pressure column of a three-column system—or as an alternative on in addition. oxygen from the single column of a single-column system or from the MDS or intermediate pressure column of a three-column system and/or from the low-pressure column of a two-column or three-column system) is taken in liquid form from one of the columns of the three-column system or from a condenser connected with one of these columns; is brought to an increased pressure in the liquid condition; is evaporated or pseudo-evaporated (at a supercritical pressure) in an indirect heat exchange with a first heat transfer medium flow; and finally obtained as a gaseous pressure product. The first heat transfer medium is frequently formed by charge air and/or nitrogen. The indirect heat exchange can take place in a separate heat exchanger or in the main heat exchanger in which the cooling of the charge air also takes place.

Internal condensation processes of this type are known, for example, from German Patent Documents DE 830805, DE 901542 (=U.S. Pat. No. 2,712,738/U.S. Pat. No. 2,784,572), DE 952908, DE 1103363 (=U.S. Pat. No. 3,083,544), DE 1112997 (=U.S. Patent Document US 32114925), DE 1124529, DE 1117616 (=U.S. Pat. No. 3,280,574), DE 1226616 (=U.S. Pat. No. 3,216,206), DE 1229561 (=U.S. Pat. No. 3,222,878), DE 1199293, DE 1187248 (=U.S. Pat. No. 3,371,496), DE 1235347, DE 1258882 (=U.S. Pat. No. 3,426,543), DE 1263037 (=U.S. Pat. No. 3,401,531), DE 1501722 (=U.S. Pat. No. 3,416,323), DE 1501723 (=U.S. Pat. No. 3,500,651), DE 2535132 (=U.S. Pat. No. 4,279,631), DE 2646690, European Patent Document EP 93448 B1 (=U.S. Pat. No. 4,555,256), European Patent Document EP 384483 B1 (=U.S. Pat. No. 5,036,672), European Patent Document 505812 B1 (—U.S. Pat. No. 5,263,328), European Patent Document 716280 B1 (=U.S. Pat. No. 5,644,934), European Patent Document EP 842385 B1 (=U.S. Pat. No. 5,953,937), European Patent Document EP 758733 B1 (=U.S. Pat. No. 5,845,517) European Patent Document EP 895045 B1 (=U.S. Pat. No. 6,038,885), German Patent Document DE 19803437 A1, European Patent Document 949471 B1 (=U.S. Pat. No. 6,185,960 B1), European Patent Document 955509 A1 (=U.S. Pat. No. 6,196,022 B1), European Patent Document 1031804 A1 (=U.S. Pat. No. 6,314,755), German Patent Document DE 19909744 A1, European Patent Document 1067345 A1=U.S. Pat. No. 6,336,345) European Patent Document 1074805 A1 (U.S. Pat. No. 6,332,337), German Patent Document 19954593 A1, European Patent Document EP 1134525 A1 (=U.S. Pat. No. 6,477,860), German Patent Document DE 10013073 A1, European Patent Documents EP 1139046 A1, EP 1146301 A1, EP 1150082 A1, EP 1213552 A1, German Patent Document DE 10115258 A1, European Patent Document 1284404 A1 (=U.S. Patent Document US 2003051504 A1), European Patent Document EP 1308680 A1 (=U.S. Pat. No. 6,612,129 B2), German Patent Document DE 10213212 A1, German Patent Document 10213211 A1, European Patent Document 1357342 A1 or German Patent Document DE 10238282 A1.

The pressure increase in the liquid can be achieved by any known measure, for example, by means of a pump, the utilization of a hydrostatic potential, and/or the pressure build-up evaporation in a tank.

Here, the term “evaporating” includes a pseudo-evaporation under a supercritical pressure. The pressure to which the product liquid is pressurized can therefore also be above the critical pressure; as may the pressure of the heat transfer medium which is (pseudo)condensed against the nitrogen.

From European Patent Document EP 895045 B1 (=U.S. Pat. No. 6,038,885), it is known to utilize a liquid tank and connected devices for increasing the pressure in the liquid tank for the internal condensation as well as for an emergency operation which, in the event of a failure of the distillation column system, permits a continuation of the delivery of gaseous pressure product. In the emergency operation, the pressurized product liquid is evaporated against another second heat transfer medium flow, normally in an atmospheric or in a water bath evaporator. This integration has many advantages. However, if maintenance or revision work becomes necessary at the liquid tank, the entire system has to be switched off, and neither the normal nor the emergency operation can be implemented.

It is therefore an object of the invention to further increase the utility of the above-described system.

This object is achieved in that, in the case of the process of the invention, a third operating condition, the bypass operation, is provided. Here, the product fraction withdrawn in a liquid state from the distillation column system is guided past the liquid tank, is pressurized in the pump set in the liquid condition to an increased pressure, is evaporated in the indirect heat exchange with a first heat transfer medium flow and is withdrawn as a gaseous pressure product. For the pressure increase and the evaporation basically separate devices can be provided. However, as a rule, it is more advantageous in the bypass operation to utilize the same devices for this purpose (for example, pumps and heat exchangers) and the same heat transfer medium flow as in the normal operation.

Thus, within the scope of the invention, the internal condensation can also be continued during times in which the tank is not available. The system can continue to supply gaseous pressure product. However, the bypass operation can also be utilized at temporary fluctuations of the purity of the liquid product fraction from the distillation column system in order to prevent a contamination of the product stored in the liquid tank; in this case also, it may be favorable to bypass the tank in the manner according to the invention.

The devices for the pressure increase in the liquid condition mostly consist of pumps. In principle, it is conceivable to use a single pump. However, for reasons of redundancy, a pump set is frequently used, that is, a plurality of pumps connected in parallel. In this case, a pump set may have approximately two or three pumps with a 50% capacity respectively; in the case of three (or more) pumps, one is only held in a standby position in order to take over the task of one of the other pumps in the event of a disturbance of their operation.

Irrespective of their number, the pump quantity delivery is generally regulated by one pump bypass respectively per individual pump, by means of which the excess quantity of pumped liquid is expanded and is returned into the liquid tank.

In the event that the pressure increase in the liquid condition in the normal operation is carried out in a pump set which has one or more parallel-connected individual pumps, at least one individual pump having a first pump bypass by way of which at least at times a portion of the product liquid exiting from the pump is expanded and returned into the liquid tank, and that the same pump set is utilized also in the bypass operation for the pressure increase in the liquid condition, it is therefore advantageous, for at least one individual pump, to have, in addition to the first pump bypass, a second pump bypass by way of which in the bypass operation, at least at times, a portion of the product liquid exiting from the pump is expanded, is guided past the liquid tank and is returned to the inlet of the pump set. Preferably several or all pumps of the pump set each have a first and a second pump bypass in the above-mentioned sense.

The invention can also be applied to multibranch distillation column systems which have a common liquid tank, as described in German Patent Application 102004006283, which is no prior publication, and the applications corresponding thereto. In this case, the product fraction is introduced from two or more branches of the distillation column system into the liquid tank. The liquid tank as well as the devices for the pressure increase are jointly utilized by the two or two or more branches of the distillation column system.

The invention as well as additional details of the invention will be explained in the following by means of an embodiment schematically illustrated in the drawing.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The single drawing figure schematically depicts a system constructed according to preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

From an air separation system 1, which has a “distillation column system”, a “product fraction” 2 is withdrawn in a liquid state. In the example shown, the distillation column system is constructed as a 2-column system with a high-pressure column and a low-pressure column, and the product fraction 2 is formed by liquid oxygen from the sump of the low-pressure column.

A schematically depicted control unit CU is operable to control the valves of the system to carry out the processes described herein.

In the normal operation, the liquid oxygen 2 is fed through an opened valve 51 by way of a pipe 3 into a liquid tank 4. Simultaneously, liquid oxygen 5 is withdrawn from the liquid tank (valve 52 is also opened) and is fed to a pump set 6 which consists of a single pump or of several parallel-connected individual pumps. There, the liquid is brought to approximately the desired product pressure and is guided by way the pipe 7 (valve 53 open) to a first evaporator 8, and is evaporated there against a “first heat transfer medium flow”. The latter is preferably formed by a correspondingly highly condensed flow of charge air for the air separation system 1, or by a high-pressure nitrogen from the air separation system 1. In the embodiment shown, the evaporator 8 is formed by the main heat exchanger of the air separation system 1, in which is charge air is cooled to the fractionating temperature. As an alternative, it can also be constructed as a heat exchanger, such as a secondary condenser, separated from the main heat exchanger. By way of the pipe 9, oxygen exits as a gaseous pressure product and can be fed to a consuming device or a distributing system.

A pump bypass 10 is used for regulating the pumped quantity. By way of this pipe and a throttle valve 54, as a rule, a portion of the pumped quantity is returned into the liquid tank 4. Only one pump bypass 10 is illustrated in the drawing. If the pump set 6 consists of more than a single pump, each individual pump has a separate pipe with a separate throttle valve and shut-off valve.

If the air separation system 1 fails as a result of a planned or unplanned operational interruption, the system is switched to an emergency operation. For this purpose, valves 51 and 53 are closed and valve 61 is opened. As a result, liquid oxygen stored in the liquid tank 4 flows by way of a pipe 60 to a second evaporator 62 which evaporates by means of a “second heat transfer medium flow” which differs from the first heat transfer medium flow. The second evaporator 62 is constructed, for example, as an atmospheric evaporator or as a water bath evaporator. In the emergency operation, oxygen leaves the system as a gaseous pressure product by way of the pipe 63 and is guided to a consuming device or a distributing system.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. Process for obtaining a gaseous pressure product by cryogenic separation of air, wherein, in a normal operation: charge air is condensed, cooled and fed to a distillation column system, a product fraction is withdrawn in a liquid state from the distillation column system and is introduced into a liquid tank, product liquid is removed from the liquid tank, via a pump set having one or more parallel-connected individual pumps, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a first heat transfer medium flow, and is withdrawn as a gaseous pressure product, wherein, in an emergency operation: product liquid is removed from the liquid tank, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange with a second heat transfer medium flow and is withdrawn as a gaseous pressure product, and wherein in a bypass operation: the product fraction withdrawn in a liquid state from the distillation column system is guided past the liquid tank, is pressurized in the pump set in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange, and is withdrawn as a gaseous pressure product.
 2. Method according to claim 1, wherein at least one individual pump of the pump set has a first pump bypass, by way of which, in the normal operation, at least at times, a portion of the product liquid exiting from the pump is expanded and is returned into the liquid tank, and wherein at least one individual pump, in addition to the first pump bypass, has a second pump bypass, by way of which, in the bypass operation, at least at times, a portion of the product liquid exiting from the pump is expanded, is guided past the liquid tank, and is returned into the distillation column system.
 3. Process according to claim 1, wherein the distillation column system is constructed with two or more branches, the product fraction being introduced from the two or more branches of the distillation column system into the liquid tank.
 4. Process according to claim 2, wherein the distillation column system is constructed with two or more branches, the product fraction being introduced from the two or more branches of the distillation column system into the liquid tank.
 5. System for obtaining a gaseous pressure product by cryogenic separation of air having a distillation column system, a liquid tank, a pump set having one or more parallel-connected individual pumps, a main heat exchanger and an emergency supply heat exchanger, and a regulating device which regulates the operation of the system in a normal operation and in an emergency operation, wherein, in the normal operation: charge air is condensed, cooled and fed to the distillation column system, a product fraction is withdrawn in a liquid state from the distillation column system and is introduced into the liquid tank, product liquid is removed from the liquid tank via the pump set, is brought in the liquid condition to an increased pressure, is evaporated in the indirect heat exchange with a first heat transfer medium flow in the main heat exchanger, and is withdrawn as a gaseous pressure product, and in the emergency operation: product liquid is removed from the liquid tank, is brought in the liquid condition to an increased pressure via the pump set, is evaporated in an indirect heat exchange with a second heat transfer medium flow in the emergency supply heat exchanger and is withdrawn as a gaseous pressure product, and wherein in addition, the regulating device regulates the operation of the system in a bypass operation such that, in the bypass operation: the product fraction withdrawn in a liquid state from the distillation column system is guided past the liquid tank, is brought in the liquid condition to an increased pressure, is evaporated in an indirect heat exchange, and is withdrawn as a gaseous pressure product.
 6. A system according to claim 5, wherein at least one individual pump of the pump set has a first pump bypass, by way of which, in the normal operation, at least at times, a portion of the product liquid exiting from the pump is expanded and is returned into the liquid tank, and wherein at least one individual pump, in addition to the first pump bypass, has a second pump bypass, by way of which, in the bypass operation, at least at times, a portion of the product liquid exiting from the pump is expanded, is guided past the liquid tank, and is returned into the distillation column system.
 7. A system according to claim 5, wherein the distillation column system is constructed with two or more branches, the product fraction being introduced from the two or more branches of the distillation column system into the liquid tank.
 8. A system according to claim 6, wherein the distillation column system is constructed with two or more branches, the product fraction being introduced from the two or more branches of the distillation column system into the liquid tank. 